说明

执行 get 查询，可以传入 多个 rowkey

相当于 SQL 的：select * from ... where id in ('1','2','3')

底层实现

hbase java api，批量操作的底层，都是调用 batch 方法

批量 get() 方法在 HTable 类中，声明如下：

@Override
public Result[] get(List<Get> gets) throws IOException {
    if (gets.size() == 1) {
      return new Result[]{get(gets.get(0))};
    }
    try {
      Object[] r1 = new Object[gets.size()];
      batch((List<? extends Row>)gets, r1, readRpcTimeoutMs);
      // Translate.
      Result [] results = new Result[r1.length];
      int i = 0;
      for (Object obj: r1) {
        // Batch ensures if there is a failure we get an exception instead
        results[i++] = (Result)obj;
      }
      return results;
    } catch (InterruptedException e) {
      throw (InterruptedIOException)new InterruptedIOException().initCause(e);
    }
}

解释： 将 多个 Get 对象放入 List 中，然后将 list 传入 get 方法，返回 Result[]

案例

查询 rowkey 是 1001、1002 的数据

相当于 SQL中的: select * from book where id in ('1001','1002')

添加测试数据

清空表：

truncate 'student'

添加数据：

put 'book','1001','c1:title','htlm从入门到放弃'
put 'book','1001','c1:author','lucy'
put 'book','1001','c1:price','097.50'

put 'book','1002','c1:title','css从入门到放弃'
put 'book','1002','c1:author','lili'
put 'book','1002','c1:price','099.90'

put 'book','1003','c1:title','hadoop从入门到放弃'
put 'book','1003','c1:author','韩梅梅'
put 'book','1003','c1:price','190.00'

关键代码

导包：

import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.client.Get;
import org.apache.hadoop.hbase.client.Put;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.client.Table;
import org.apache.hadoop.hbase.util.Bytes;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

方法：

public List<RowData> getBatch(String tableName, String[] rowkeys) throws IOException {
    TableName tn = TableName.valueOf(tableName);
    //admin封装对表的操作，创建表、删除表、禁用表、启用表
    Table table = conn.getTable(tn);
    List<Get> list = new ArrayList<>();
    for (String item : rowkeys) {
        Get get = new Get(Bytes.toBytes(item));
        list.add(get);
    }
    List<RowData> retList = new ArrayList<>();
    //执行get操作
    Result[] results = table.get(list);
    for (Result result : results) {
        //获取rowkey
        String rowkey = Bytes.toString(result.getRow());
        RowData rowData = new RowData(rowkey);
        List<Cell> cells = result.listCells();
        if (cells != null) {
            for (Cell item : cells) {
                String family = Bytes.toString(CellUtil.cloneFamily(item));
                String qualifier = Bytes.toString(CellUtil.cloneQualifier(item));
                String value = Bytes.toString(CellUtil.cloneValue(item));
                CellData cellData = new CellData(family, qualifier, rowkey, item.getTimestamp(), value);
                rowData.addCellData(cellData);
            }
            retList.add(rowData);
        }
    }
    table.close();
    return retList;
}

测试

HbaseUtils2_getBatch utils=new HbaseUtils2_getBatch();
utils.connect("hadoop1,hadoop2,hadoop3","2181");
String[] rowkeys = {"1020","1021"};
List<RowData> list = utils.getBatch("book", rowkeys);

System.out.println("-------------------------");
for (RowData rowData : list){
    List<CellData> cellDatas = rowData.getCellDatas();

    for(CellData cellData :cellDatas){
        System.out.print(cellData.getFamily()+":"+cellData.getQualifier()+"="+cellData.getValue()+" | ");
    }
    System.out.println("\n-------------------------");
}
utils.close();
}